Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted aircharge delivered to the engine intake manifold and improving peak power outputs. The use of a compressor allows a smaller displacement engine to provide as much power as a larger displacement engine, but with additional fuel economy benefits. However, compressors may be prone to surge. Surge can lead to noise, vibration, and harshness (NVH) issues such as undesirable noise from the engine intake system. In extreme cases, surge may result in compressor damage. To address compressor surge, engine systems may include a continuously variable compressor recirculation valve (CCRV) coupled across the compressor to enable rapid decaying of boost pressure. The CCRV may recirculate compressed air from the compressor outlet to the compressor inlet. In an example, the CCRV may be configured similar to an intake throttle butterfly valve so that it can be actuated fully open, fully closed, or positions there-between.
Throughout the life of an engine, deposits such as sludge may accumulate on the throttle valve body and reduce the effective airflow rate for a given throttle plate angle. As an example, the inventors have identified that not only can sludge accumulate, but that it can reduce airflow through across a range of throttle valve angles.
Other attempts to control CCRV for boost control include adjusting a wastegate and/or intake throttle other than CCRV in response to CCRV degradation. One example approach is shown by Jankovic et al. in US 2014/0260241 A1. Therein, CCRV degradation is determined based on response of the CCRV to a command of changing its position, where the CCRV response is measured by a position sensor.
However, the inventors herein have recognized that even adjusting other actuators may not sufficiently address the issue of sludge accumulation on the valve body. Further, even if the CCRV position is sensed, sludge can still adversely affect the flow control. For example, the valve can be accurately controlled to the desired position, yet due to sludge buildup the flow for the desired position is less than would otherwise be expected and thus overall flow control can degrade. Moreover, because sludge may gradually accumulate on the valve body, the CCRV may still be operable even though the response of CCRV to the command is not accurate.
In one example, the issues described above may be addressed by a method comprising: adjusting a position of a valve located inside a compressor recirculation passage of an engine based on a recirculation flow, the recirculation flow based on a difference between total intake flow downstream of a compressor recirculation passage outlet but upstream of the passage inlet, and total engine flow entering engine cylinders.
In this way, recirculation flow may be estimated, and compressor surge may be addressed by accurately controlling the recirculation flow through the CCRV. Moreover, sludge accumulation on the valve body may be estimated based on the estimated recirculation flow.
As one example, a total intake flow rate is measured by a mass air flow sensor positioned downstream of a compressor recirculation passage outlet but upstream of the passage inlet. A recirculation flow in the compressor recirculation passage may be estimated based on the difference between the measured total intake flow and a total engine flow entering engine cylinders. The total amount of sludge accumulation on a valve positioned in the compressor recirculation passage may be estimated based on the recirculation flow. The valve position may then be adjusted based on the estimated total amount of sludge accumulation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.